The long term objective of this research is to determine the mechanisms by which the invertebrate nuclear receptor, ultraspiracle, transduces the regulatory signals of its endogenous ligands(s) into pathways for transcriptional activation. The proposed research builds upon their recent studies that have demonstrated that two natural dipteran epoxymethylfarnesoates bind with specificity to ultraspiracle so as to cause conformational change in that receptor, while closely related farnesoid pathway metabolites do not have this interaction with USP.